Diseases, acute injuries, and other conditions can adversely affect blood flow to and in the limbs. In a general sense, agents and factors that may affect and lower circulation to the limbs, also known as peripheral circulation, include certain drugs, especially vasoconstrictors, poor perfusion per se due to shock, such as results from low blood volume, or septic or cardiogenic shock, certain traumas, external pressure (as from burns), hypothermia, and other mechanical abnormalities or injuries. In particular, decreased peripheral circulation may be caused by a number of disorders within the body including, but not limited to, atherosclerosis, Raynaud's disease, Buerger's disease, chronic obstructive pulmonary diseases (COPD), and embolic occlusive disease.
Poor blood flow reduces the amount of oxygen that is carried in the blood stream to cells. Emergency rooms, intensive care units, burn units, operating rooms, and ambulances treat a variety of critically ill patients in need of continuous monitoring of real time hemoglobin saturation and/or blood pressure readings. If oxygen levels in the blood become very low at peripheral sites, a variety of problems may occur which include inadequate resuscitation, cell death or necrosis that can lead to non-healing lesions, gangrene and amputation of limbs. Also, in progressive diabetes and other conditions that may result in atherosclerosis that affect peripheral circulation and perfusion, non-invasive measurement of circulation and/or resistance status is useful to monitor the progression of the disease and the effectiveness of treatments.
Also, many patients, especially among the elderly, are on chronic oxygen therapy; they are in need of supplemental oxygen on a routine basis. Such patients may have impaired and/or diminished cardiopulmonary capacity. When such patients are ambulatory, their supply of oxygen (usually a tank of compressed oxygen or liquid oxygen) must be transported with them wherever they travel. Oxygen from such supply passes through a regulator and thence, typically, via a tube to the nose where it is inhaled (e.g., via a nasal cannula or the like). Alternatively, the oxygen may be delivered by a cannula directly into the trachea (transtracheal supplemental oxygen). Embodiments of the present invention combine the supply of oxygen or oxygen-rich air with a pulse oximeter that adjusts the release of the supply to better match the actual bodily requirement based on the measured blood oxygen saturation. A pulse oximeter that receives the signal from the pulse oximeter probe is located a distance from the probe itself, and provides a blood oxygen saturation measurement to the user (and/or to a remote monitor), and/or, in certain embodiments acts to adjust the inflow rate or quality of the oxygen or oxygen-rich gas being supplied. This, depending on each particular user and his/her baseline settings, can either extend the life of a given supply of compressed oxygen or oxygen-rich gas, or provide oxygen or oxygen-rich gas on a more accurate, as-needed basis, in the latter case improving the health and/or performance of the user.
As to the latter benefit of this aspect of the present invention, provision of an accurate, as-needed supply of oxygen reduces the risk of and/or alleviates problems of hypoxia that are associated with improper adjustment of supplemental oxygen to patients in need thereof. Hypoxia, low oxygen delivery, or hypoxemia, low oxygen tension in the blood, cause a number of maladies including polycythemia (increased hematocrit) which leads to abnormal clotting. Polycythemia is a compensatory mechanism to chronic hypoxemia that typically builds up over weeks to months. It is typical in persons with chronic lung disease (and also persons living at high altitudes).
A more immediate, primary physiologic compensatory response to oxygen deficit is increased cardiac output. This is normal, such as during increased physical exertion. However, in persons who have impaired cardiocirculatory reserve, increased cardiac output in response to low arterial oxygen level can, under certain circumstances, eventually lead to death. The second immediate physiologic compensatory response to oxygen deficit is the extraction of more oxygen from hemoglobin within the capillaries of the body's organs. This normally happens either during an increase in oxygen demand (i.e., exercise, fever, shivering, etc.), or during normal demand but decreased oxygen delivery (i.e., due to inadequate blood flow, anemia, hypoxia). In such instances, metabolically active cells draw additional oxygen from the red blood cells which ultimately resulting in a decrease in the mixed venous blood's oxygen saturation falling from a typical 65% to 80% level to levels as low as 32% (see Hemodynamic Monitoring—Invasive and Noninvasive Clinical Application, by Gloria Oblouk Darovic, 3rd Ed., 2002, Chapter 12). Chronic hypoxemia can lead to a switch by metabolically active cells to anaerobic metabolism, which, especially in patients with limited cardiopulmonary reserve, can lead to lactic acidosis and eventually death.
Hypoxemia also causes cognitive dysfunction either acutely or chronically which can lead to early dementia and death. Generally, based on the compensatory mechanisms and effects on body tissues, chronic hypoxemia may affect all organs in the body leading to failure of any or all organs.
In general, blood oxygen levels are currently measured by pulse oximetry, which can be divided into transmittance and reflectance types. Transmittance, or transillumination oximetry, involves the process whereby a sensor measures light extinction as light passes through a portion of blood-perfused tissue. Light is transmitted from one side of a portion of blood-perfused tissue, and is recorded by a sensor situated across the portion of tissue. Reflectance oximetry, on the other hand, has both the light source and the sensor on one side of the tissue, and measures reflectance back from the tissue. For both types of oximetry, multiple signals from the light sensor, or detector, are used to estimate the oxygen saturation and pulse rate from changes in absorption of the light detected throughout blood pulse cycles. The technology is based on the differential absorbence of different wavelengths of light by different species of hemoglobin.
Conventional pulse oximetry measurement in certain classes of patients, for instance severely burned patients, can be a significant challenge, yet this monitoring data is vital in operating room and intensive care settings. Most current pulse oximetric approaches depend upon available peripheral sites permitting transillumination oximetry which is sufficient for most surgical conditions and procedures. However, in one example, patients with severe burns often have only a few sites suitable for the effective placement of the transmitting pulse oximeter sensor. These patients often have severe circulatory compromise rendering the current peripheral pulse oximeters less effective.
The technology of pulse oximeters is well known (See “Pulse Oximetry: Principles and Limitations,” J. E. Sinex, Am. J. Emerg. Med., 1999, 17:59–66). Pulse oximetry includes a sensor, or probe, with light source(s) generating at least two different wavelengths of light, and a detector placed across a section of vascularized tissue such as on a finger, toe, or ear lobe. Pulse oximetry relies on the differential absorbance of the electromagnetic spectrum by different species of hemoglobin. In a typical system, two distinct wavelength bands, for instance 650–670 nm and 880–940 nm, are used to detect the relative concentrations of oxygenated hemoglobin (oxyhemoglobin) and non-oxygenated reduced hemoglobin, respectively. The background absorbance of tissues and venous blood absorbs, scatters and otherwise interferes with the absorbance directly attributable to the arterial blood. However, due to the enlargement of the cross-sectional area of the arterial vessels during the surge of blood from ventricular contraction, a relatively larger signal can be attributed to the absorbance of arterial hemoglobin during the systole.
By averaging multiple readings and determining the ratio peaks of specific wavelengths, a software program can estimate the relative absorbance due to the arterial blood flow. First, by calculating the differences in absorption signals over short periods of time during which the systole and diastole are detected, the peak net absorbance by oxygenated hemoglobin is established. The signals typically are in the hundreds per second. The software subtracts the major “noise” components (from non-arterial sources) from the peak signals to arrive at the relative contribution from the arterial pulse. As appropriate, an algorithm system may average readings, remove outliers, and/or increase or decrease the light intensity to obtain a result. The results from one site provide a measurement of arterial oxygen saturation at that site, and also allows calculation of the shape of the pulse at the placement site of the probe, which can be developed into a plethysymograph. Among the various sources of signal interference and modification, it is noted that the shape of red blood cells changes during passage through arterial and venous vessels. This change in shape affects scattering of the light used in pulse oximetry. Algorithms are designed to correct for such scattering.
More sophisticated pulse oximetry systems detect at more than merely two bands, such as the 650–670 nm and 880–940 nm wavelength bands. For instance, the pulse oximetry article from a uni-erlangen web site stated that four LEDs, at 630, 680, 730 and 780 nm, each with 10 nm bandwidths, can determine the four common species of hemoglobin. The article further calculated that the detection of nine wavelengths in the range of 600 to 850 nm would provide greater accuracy in assessing these four forms of hemoglobin, oxyhemoglobin (O2Hb), reduced hemoglobin (HHb), methemoglobin (MetHb), and carboxyhemoglobin (COHb). As used in the present invention, the term “pulse oximeter” or “oximeter” is meant to include all designs and types of pulse oximeters, including current and later developed models that transmit and detect at more than two wavelengths associated with absorption differences of these hemoglobin species.
At present, peripheral vascular resistance can only be measured invasively, or non-invasively by skilled technicians using Doppler flow devices. The use of Doppler and Doppler waveform analysis is now a standard investigation technique for obtaining measurements in blood flow resistance patients with possible circulatory disorders. For example, Dougherty and Lowry (J. Med. Eng. Technol., 1992: 16:123–128) combined a reflectance oximeter and a laser Doppler flowmeter to continuously measure both blood oxygen saturation and perfusion.
A number of patents have been issued directed to monitors, sensors and probes for use in pulse oximetry procedures. For instance, U.S. Pat. No. 6,334,065, issued on Dec. 25, 2001 to Al-Ali, et al., discloses a stereo pulse oximeter that provides for simultaneous, non-invasive oxygen status and photoplethysmograph measurements at both single and multiple sites. The invention is directed to the detection of neonatal heart abnormalities, particularly related to defects of heart-associated vessels, and specifically directed to Persistent Pulmonary Hypertension in Neonates (PHHN), Patent Ductus Arteriosis (PDA), and Aortic Coarctation. All of these conditions result in a flow of differentially oxygenated blood to different peripheral extremities. For instance, in PHHN and PDA, the blood that flows to the right hand is unaffected by the abnormal shunt that results in less oxygenated blood flowing to other areas. Thus, comparison of oxygen saturation values between a pulse oximeter sensor at the right hand and at, for instance, a foot site, is stated to detect or confirm the diagnosis of such neonatal heart abnormalities. Continuous monitoring with such pulse oximetry also is proposed, to provide feedback on the effectiveness of treatments or surgery to deal with these neonatal cardio/cardiopulmonary conditions. U.S. Pat. No. 6,334,065 does not address the use of two probes for detection, confirmation, or monitoring of perfusion- and resistance-related conditions in the patient. Such conditions would not be expected in a neonatal patient, and are instead more likely found in aging patients and in patients with certain accident conditions unrelated to neonatal heart and heart-associated vessel anomalies.
U.S. Pat. No. 6,263,223 was issued on Jul. 17, 2001 to Shepard et al., and teaches a method for taking reflectance oximeter readings within the nasal cavity and oral cavity and down through the posterior pharynx. Whereas the conventional transillumination pulse oximeter probe detects the light not absorbed or scattered as it crosses a vascularized tissue covered by skin (i.e., the LEDs and photodetector are separated by the tissue), a reflectance oximeter probe detects light by backscattering of light that traverses vascularized tissue not bounded by skin and is reflected back to a detector positioned on the same side of the tissue as the LEDs (e.g., on tissue in the mouth). The method includes inserting a reflectance pulse oximeter sensor into a cavity within a subject's skull and contacting a capillary bed disposed in the cavity with the reflectance pulse oximeter sensor. The method uses standard pulse oximeter sensor probes placed over capillary beds close to a buccal surface, posterior soft palate, hard palate or proximal posterior pharynx, including the tongue, nares or cheek. Reflectance pulse oximetry at these sites determines arterial oxygen saturation. One major problem with this device is that it does not permit cross-site comparisons of oxygen saturation values between several tissue sites. In addition, the pulse oximeter device used in this invention is an elongated tube that is inserted far into the nasal or oral cavity down into the pharynx, which is a highly invasive procedure.
U.S. Pat. No. 4,928,691, issued on May 29, 1990 to Nicolson et al., and currently withdrawn, discloses a non-invasive, electro-optical sensor probe and a method for its use. The sensor is enabled to measure light extinction during transillumination of a portion of blood-perfused tissue and to calculate the oxygen saturation and pulse rate from changes in absorption of the light detected. The sensor probe is placed at a central site such as the tongue, cheek, gum or lip of the patient and provides continuous assessment of arterial oxygen saturation and pulse rate. The sensor is malleable and extremely flexible, and is stated to conform to the structure of the skin and underlying tissue. U.S. Pat. No. 4,928,691 states that measurement at the preferred central sites provide accurate oxygen saturation and pulse readings for “patients with lowered or inconsistent peripheral perfusion.” Critically, the probes according to U.S. Pat. No. 4,928,691 are highly flexible, leading to a high likelihood that upon typical movement of the patient there would be mal-alignment between the light source(s) and sensor, resulting in skewed, non-usable, or unreliable signals and results. Also, there is no teaching or suggestion to compare oxygen saturation values between several tissue sites to identify, characterize, or monitor peripheral perfusion conditions in such patients.
U.S. Pat. No. 5,218,962 was issued on Jun. 15, 1993 to Mannheimer et al., teaches a pulse oximetry system which monitors oxygen saturation and pulse rates by sensing the blood characteristics at two or more peripheral sites. The device includes one or more pulse oximetry probes which passes light through unique regions of tissue and a sensor which detects the amount of light passing through the tissue, and an instrument that independently calculates oxygen saturation level within each region. The difference in values represents how much the oxygen saturation of the first region of tissue differs from the oxygen saturation of the second region of tissue. When the difference between the two values is below a set threshold, the '962 patent attributes this to a sufficiently high probability that the value is true, and displays an oxygen saturation value that is a function of the two independent values. Where there is a difference greater than a set threshold, no oxygen saturation value is displayed. Thus, the '962 patent attributes substantial differences between two sites to be due to error, rather than to an indication of a problem with peripheral perfusion and/or resistance.
U.S. Pat. No. 5,335,659, issued on Aug. 9, 1994 to Pologe, teaches a nasal septum probe for photoplethysmographic measurements that clips onto a patient's nasal septum. Pulse oximetry is one of the stated applications for the apparatus. Structurally, the apparatus disclosed and claimed in the '659 patent has a body, or housing, from which two probe arms extend, these arms being sized to enter the nostrils of a nose. One arm bears at least two light sources, and the other arm bears at least one light detector. The probe apparatus securely grasps the nasal septum in such a way that there is contact on both sides of the nasal septum at the same time with both the light sources and the light detector. In all embodiments, the light sources and the light detector actually protrude from the main body of the respective probe arm, and are positioned to exert pressure upon and indent the tissue of the nasal septum. In some embodiments and all claims, a supply of gas is also provided from a source through a support means and to the nasal septum. However, the '659 patent does not disclose a nasal pulse oximeter probe that does not need to press into the tissue of the nasal septum in order to obtain reliable pulse oximetry data, nor a probe that includes an angle, or bend, to reach a desired highly vascular plexus on the septum.
WIPO Application No. WO0021435A1, to Barnett et al., was published Apr. 20, 2000. This publication teaches a non-invasive spectrophotometric examination and monitoring of blood metabolites in multiple tissue regions on an ongoing and instantaneous basis. The method includes attaching multiple sensors to a patient and coupling each sensor to a control and processing station enabled to analyze signals conveyed thereto. The control and processing station visually displays the data from multiple sites for direct mutual comparison of oxygen saturation values from multiple sites. A key aspect of the invention is the use of a “near” and a “far” (or “deep”) detector at each detection site. Based on the positioning of the light-generating devices and the near and far sensors, the far sensor receives absorption signals from deeper inside the brain tissue. In a basic configuration, the “near” sensor, or detector, principally receives light from the source whose mean path length is primarily confined to the layers of skin, tissue, and skull, while the “far” detector which receives light sprectra that have followed a longer mean path length and traversed a substantial amount of brain tissue in addition to the bone and tissue traversed by the “near” detector. Other configurations indicate receptors receive signals from sources across the entire brain cross-section. This is stated to provide information about, by calculation differences, the condition of the deeper tissue, in particular the brain. The method is directed to compare oxygen saturation values for cerebral tissue, such as comparing the two hemispheres during surgery. The WO0021435A1 invention distinguishes itself from standard pulse oximetry of arteries close to the surface of the body, and focuses primarily on analysis of deeper tissues and organs. The application does not teach a method to measure “surface” peripheral or central tissue sites for development of information regarding perfusion status.
WIPO Application No. WO0154575A1, to Chen et al., was published on Aug. 2, 2001. This publication teaches a non-invasive apparatus and method for monitoring the blood pressure of a subject. A monitor is used for continuous, non-invasive blood pressure monitoring. The method includes using sensors to detect a first blood pressure pulse signal at a first location on patient and detecting a second blood pressure pulse signal at a second location on the patient; measuring a time difference between corresponding points on the first and second blood pressure pulse signals; and, computing an estimated blood pressure from the time difference. The first and second sensors are placed at locations such as a finger, toe, wrist, earlobe, ankle, nose, lip, or any other part of the body where blood vessels are close to the surface of the skin of a patient where a blood pressure pulse wave can be readily detected by the sensors, and/or where a pressure pulse wave from the patient's heart takes a different amount of time to propagate to the first location than to the second location.
In one regard, a superior monitor system would be able to provide real-time continuous measurements of signals that would be analyzed to provide arterial oxygen saturation, blood pressure, and pulse rate. A superior monitor system would utilize at least two pulse oximeter probes, one of which is placed at a highly perfused central tissue, such as the lip, tongue, nares, cheek, and a second probe placed at a typically less perfused areas such as a finger or toe. Also, in some situations, a peripheral probe may be placed at sites in or distal from areas that may be or are affected by disease- or accident-related diminished blood perfusion to tissues.
An additional aspect of a superior oximeter system provides both an inflow means of oxygen or oxygen-rich gas to a patient in need thereof, and an integral or adjoining pulse oximeter probe. This aspect is in conjunction with the above-described two pulse oximeter probe system, or in a system that only has one oximeter probe. In either case, one pulse oximeter probe, positioned at the nose or mouth, detects the levels of oxygenation saturation of blood in the patient, and detection of low or lowering oxygenation saturation levels results in one or more of: setting off a local or remote alarm or message; increasing the flow of oxygen or oxygen-rich gas to said patient. Likewise, detection of higher or increasing oxygenation levels results in one or more of: setting off a local or remote alarm or message; decreasing the flow of oxygen or oxygen-rich gas to said patient. Preferably, the pulse oximeter probe at the nose or mouth is integral with the delivery means of the oxygen or oxygen-rich gas. Preferably, the control of oxygenation levels is by signaling to (manually or automatically) adjust a valving mechanism that controls output flow from a source of auxiliary of oxygen or oxygen-rich gas. By such feedback mechanism the quantity of oxygen or oxygen-rich gas is conserved, and the needs of such patient are more closely attuned to the fluctuations in oxygen demand during activities at varying levels of exertion during a period of time.
As to references that pertain to the combining of a pulse oximeter with a system to control the inflow of oxygen or other oxygen-rich gas to a patient in need thereof, the following U.S. patents, and references contained therein, are considered to reflect the state of the current art: U.S. Pat. Nos. 4,889,116; 5,315,990; 5,365,922; 5,388,575; 6,371,114; and 6,512,938. None of these references are specifically directed to a combined, preferably integral combined pulse oximeter sensor/nasal cannula, which, when combined with an oximeter, or with an oximeter that controls the inflow of such oxygen or other oxygen-rich gas to the patient, provide the advantages disclosed and claimed herein.
All patents, patent applications and publications (scientific, lay or otherwise) discussed or cited herein are incorporated by reference to the same extent as if each individual patent, patent application or publication was specifically and individually set forth in its entirety.